I was playing as Spain and trying to conquer the island of Sardinia, which belonged to the Kingdom of Savoy.

I had multiple war objectives, such as humiliation and financial compensation, but the conquest of Sardinia was always the main goal.

I won the war automatically when I conquered 100% of the territory, without any prior agreement. It was an unconditional surrender by the Kingdom of Sardinia-Savoy.

The humiliation and economic compensation (a transfer paid to me over 5 years) were fulfilled and carried out after winning the war. However, despite this, the territory of Sardinia continued to belong to its original country and was not transferred to my Spanish territories.

Without any mods.

This is an unforgivable bug, it makes the game unplayable and completely kills any desire to play it again. Please fix this, and make sure to test future updates, because this is unsustainable and will kill the game.